1. Field of the Invention
The present invention relates to wireless communication, and more particularly to a wireless communication apparatus, a wireless communication method thereof, and a wireless communication system employing the same, for enabling peer-to-peer communication between slave devices through master-to-slave switching.
2. Description of the Related Art
FIG. 1 is a view showing the structure of a Piconet in a general Bluetooth communication system.
In a current Bluetooth system, one unit U10 operating as a master device, and a plurality of units U20, U30, and U40 operating as slave devices form a Piconet, as shown in FIG. 1. At most, seven slave devices can participate in one Piconet for one master device U10.
In the Piconet, channels are established between the master device U10 and the slave devices U20, U30 and U40, and data is transmitted in the form of a packet. FIG. 2(a) shows the general form of the transmitted packet, and FIG. 2(b) shows the header part of the packet of FIG. 2(a) in greater detail.
Master device U10 allocates an active member address (AM_ADDR) to the slave devices U20-U40 of the Piconet. The active member address AM_ADDR of the slave devices U20, U30 and U40 is written in the header part of the packet and transmitted.
In accordance with the current Bluetooth communications, a master-driven Time Division Duplex method is used. If the master device appoints a certain slave device and transmits data to the appointed slave device, then the slave device that received the data transmits the response data to the master device.
Accordingly, slave devices only transmit data to the master device, and are unable to transmit data to other slave devices of the Piconet.
If master-to-slave switching is performed between one slave device and the master device of the Piconet, the slave device becomes a new master device and can communicate with other slave devices.
In the current Bluetooth communication system, by employing master-to-slave switching, the information of the original master device is transmitted to a new master device, and the other slave devices of the Piconet communicate according to the clock of the new master device. This is done by changing transmitter and receiver timing according to the clock of the new master device.
Next, the master-to-slave switching in the current Bluetooth system will be described in greater detail with reference to the accompanying drawings.
FIG. 3 is a diagram illustrating a signal flow during the conventional master-to-slave switching in the Piconet of FIG. 1.
First, the first unit U10, i.e., the old master device, requests master-to-slave switching to the second unit U20, i.e., one of the slave devices of the Piconet, according to a hopping sequence thereof (step S302). If the second unit U20 agrees to be a new master device, the second unit U20 sends a response signal to the old master device U10 (step S304).
Hereinafter, the first unit U10 is defined as an old master device, and the second unit U20 as a new master device.
The new master device U20 sends the old master device U10 an indication of a difference in the starts of master-to-slave slots between the new master device U20 and the old master device U10 through a time alignment Link Manager Protocol (LMP) message (step S306). The LMP message allows the old master device U10 to become synchronized with the clock of the new master device U20.
Further, the new master device U20 sends a Frequency Hopping Sequence (FHS) packet containing a new active member address AM_ADDR to the old master device U10 (step S308). Then the old master device U10 sends a FHS packet response to the new master device U20 (step S310). Accordingly, the new master device U20 exchanges the data transmission timing, namely transmitter and receiver timing, with the old master device U10.
The new master device U20 also sends the other slave devices, i.e., the third unit U30 and the fourth unit U40, the same time alignment LMP message and FHS packet that are sent to the old master device U10.
More specifically, the new master device U20 transmits the time alignment LMP message and the FHS packet to the third unit U30 (steps S312, S314). Then the new master device U20 receives a FHS response packet from the third unit U30 (step S316).
Further, the new master device U20 transmits the time alignment LMP message and the FHS packet to the fourth unit U40 (steps S318, S320). Then, the new master device U20 receives the FHS response packet from the fourth unit U40 (step S322).
Through the switching processes S312-S322 in the Piconet, the slave devices such as the third and the fourth units U30 and U40 can send and receive data in accordance with the clock of the new master device U20, and receive the active member address AM_ADDR from the new master device U20.
After receipt of the FHS response, the new master device U20 switches timing, and sends a poll packet to the third and the fourth units U30 and U40 to confirm whether the respective slave devices are switched to the timing of the new master device U20 (steps S324, S326).
FIG. 4 is a view showing the structure of the Piconet of FIG. 1, after the conventional master-to-slave switching.
As shown in FIG. 4, the second unit U20 has taken the function of the master device, while other units U10, U30, and U40 operate as slave devices in the Piconet.
Since the second unit U20, which was a slave device in the Piconet of FIG. 1, has become a master device of the Piconet of FIG. 4, the second unit U20 now can communicate with the other slave devices U10, U30 and U40 (see FIG. 4).
According to the above-described master-to-slave switching method of the current Bluetooth communication system, since the slave devices of the Piconet have to be allocated with new active member addresses (AM_ADDR) from a new master device, and change transmitter and receiving timing according to the clock information of the new master device, the procedure is very complex and requires a considerable amount of processing time.
Accordingly, there has been an increasing demand for a new communication method that would enable peer-to-peer communication between the slave devices through more rapid master-to-slave switching.